$LogPath = "C:\test\xxx"
if(-not (Test-path -Path $LogPath)){
    New-Item -ItemType Directory -Force -Path $LogPath
}
$FullFilePath = Join-Path $LogPath -ChildPath "MemoryUsage.txt"
$ComputerMemory =  Get-WmiObject -Class WIN32_OperatingSystem -ComputerName localhost
$Memory =  [math]::Round(((($ComputerMemory.TotalVisibleMemorySize - $ComputerMemory.FreePhysicalMemory)*100)/ $ComputerMemory.TotalVisibleMemorySize))

$DateStr = (Get-Date).ToString("dd.MM.yyyy HH:mm K")
Add-Content -Path $FullFilePath -value "$DateStr $memory %"