How to specify alias on YamlMember in YamlDotNet?

I need to deserialize the following YAML to my custom type. YamlAlias attribute seems to be obsolete, so I replaced it with YamlMember. It fails on deserializing the following YAML with the below exception:

    host:
      properties:
        mem_size: 2048  MB

YamlDotNet.Core.YamlException : (Line: 21, Col: 13, Idx: 524) - (Line: 21, Col: 13, Idx: 524): Exception during deserialization ----> System.Runtime.Serialization.SerializationException : Property 'mem_size' not found on type 'Toscana.Domain.HostProperties'.

public class Host
{
    public HostProperties Properties { get; set; }
}

public class HostProperties
{
    [YamlMember(typeof(DigitalStorage))]
    public string MemSize { get; set; }
}